In general, a gas boiler is a device which internally combusts liquefied petroleum gas (LPG) or liquefied natural gas (LNG) or city gas, heats water using the combustion heat generated during this combustion process, and using the circulation pump heats indoors by circulating the heated water through the indoor heating pipe, or supplies hot water to the bathroom or the kitchen.
Furthermore, the gas boiler is divided into condensing and non-condensing type according to the heat exchanger heating the heating water. Among these the condensing gas boiler uses the combustion heat to directly heat the heating water, and can also maximize thermal efficiency by reabsorbing the latent heat of condensation of the exhaust gas.
Referring to the operation of the condensing gas boiler, first, high temperature heating water heated by the combustion heat of the burner is circulated to the heating pipe by the operation of the circulation pump, and the low temperature heating water collected by passing through the heating pipe is introduced into the latent heat exchanger, and the low temperature heating water introduced into the latent heat exchanger is preheated through heat exchange with exhaust gas which has passed through the sensible heat exchanger. This preheated heating water repeats the step of flowing again into the sensible heat exchanger to be directly heated by the combustion heat of the burner, and then circulating to the heating pipe by the operation of the circulation pump as described above. In addition, by the operation of the three-way valve installed on the outlet of the heat exchanger, the water heated by the burner is circulated to the heating pipe or sent to the hot water heat exchanger to carry out heat exchange with cold water supplied through the direct water pipe and be provided as hot water.
Meanwhile, such a conventional gas boiler may have unburned gas present at the combustion chamber during initial ignition, thus the burner is operated after rotating the exhaust fan at high speed to emit the unburned gas in the combustion chamber, in order to prevent explosion ignited by the unburned gas. During this time it should be determined whether the revolutions per minute (RPM) of the exhaust fan rotating at high speed is normal. This is because the exhaust fan RPM is the standard for determining blockage in an exhaust flue, or detecting headwind flowed in or drawn in through the exhaust flue. For this reason the exhaust fan RPM is detected and compared with the preset exhaust fan RPM. In this way, when determining blockage in an exhaust flue, during the process of confirming the operating conditions of a boiler by detecting the exhaust fan RPM, the reference fan RPM is preset and saved in the microcomputer, the exhaust fan RPM is detected during initial operation of the boiler and compared with the reference fan RPM, and if the detected RPM is determined to exceed the reference fan RPM, operation of the boiler is stopped and exhaust flue blockage error is displayed.
The exhaust flue blockage is detected as above since when the exhaust flue is blocked there is no gas, that is air flow discharged by the rotating exhaust fan, thereby the exhaust fan does not perform any action, and consequently, rotational speed of the exhaust fan is accelerated even when same operating voltage is applied. Furthermore, in the event of exhaust flue blockage or strong headwind, the mixing ratio of air and gas is inadequate, resulting in incomplete combustion which leads to a large amount of carbon monoxide in the exhaust gas and unburned gas being discharged, entailing a risk of poisoning accident.
Conventionally, most gas boilers have differential pressure sensors for detecting exhaust flue blockage or headwind, etc., or adopt the method of detecting exhaust flue blockage by comparing the blower RPM with the reference RPM, or comparing the current or voltage value applied to the blower with the reference value.
However, such a method of detecting blockage in an exhaust flue can often be the cause of increase in unit costs, misdetermine a normal state as blockage in the exhaust flue due to error in an individual blower and instability of current or voltage value applied to the blower, or is unable to properly detect blockage in the exhaust flue.